Method and apparatus for determin



May 13, 1952 w. G. REYNOLDS METHOD AND APPARATUS FOR DETERMINING THEFREENESS OF WOOD PULP Filed Dec. 8, 1949 2 SHEETSSHEET l AI AHA AHHWAAINVENTOR WILL/RM G. Q'Y/VOLDS ATTORNEY y 1952 w. G. REYNOLDS 2,596,724

METHOD AND APPARATUS FOR DETERMINING THE FREENESS 0F woon PULP FiledDec. 8, 1949 2 SHEETSSHEET 2 I NVE N TOR w/z. 4mm a. KEY/V0405 RWMWATTOR NEYJ Patented May 13, 1 952 UNITED STATES PATENT OFFICE METHOD ANDAPPARATUS FOR DETERMIN- ING THE FREENESS OF WOOD PULP William G.Reynolds, Cottondale, Ala.

Application December 8, 1949, Serial No. 131,707

7 Claims.

This invention relates to a method and apparatus for determining thefreenes's and quality of hydration of pulp suspensions from which paperis manufactured.

The principal object of the invention is to provide a method andapparatus of the character designated which shall be effective todetermine the freeness of a pulp suspension independent of theconsistency thereof.

Another object is to provide a method and apparatus for testing thefreeness of pulp suspensions from the rate of deceleration in drainagebetween two areas on a moving screen.

Another object is to provide a method and apparatus for testing thequality of hydration of pulp suspensions from the change in rate ofdeceleration in drainage between two areas on a moving screen.

A still further object is to provide a method and apparatus fordetermining the freeness of pulp suspensions whereby the refiningmachines may be accurately controlled, thereby causing them to deliver apulp of uniform freeness.

Heretofore, so far as I am aware, there have been no satisfactory meansto measure accurately the freeness and quality of hydration of pulpsuspensions, particularly during the manufacture of paper on papermaking machines. Conventional testers, known to me, all measure thevelocity with which the liquid drains through a wire screen from a pulpsuspension. The thus drained liquid flows into a container having anorifice in the bottom thereof. If the pulp has high freeness the liquidwill flow through the screen faster than it can flow through the orificeand will overflow through an overflow pipe into a graduate. The volumeof liquid thus caught in the graduate is taken as the index of freenessof the pulp. Such conventional methods of testing the freeness of pulpsuspensions have been fundamentally incorrect because they determine anaverage drainage velocity-time characteristic of a pulp suspensionwhereby any freeness value obtained may represent several differentcombinations of pulp characteristics and qualities of hydration.Speaking in terms of the mathematical calculus processes, suchconventional methods amount to' a partial integration of the drainagevelocity with respect to time. This integration is partial becausedrainage velocity components which do not cause overflow into thegraduate are excluded from the integration. The drainage velocitycomponents which do not cause overflow into the graduate consists ofthat portion of the total drainage velocity which is insufficient to Idevelop a hydrostatic head large enough to cause flow of the drainedwater through the overflow pipe into the graduate. Since the freeness isdetermined by the volume overflowed into a graduate, this excludeddrainage introduces disproportion into the determination of freeness.The ratio of the excluded drainage velocity in the initial stages of thedrainage operation is relatively small. However, as the drainageoperation proceeds and the total drainage velocity decreases thatportion of the total drainage velocity insufficient to cause overflowrepresents a steadily increasing proportion of the total drainagevelocity. In order to be consistent for stocks having varyingcharacteristics, means must be provided whereby the ratio of drainagevelocity excluded from the total velocity remains constant throughoutthe operation. Later I shall show that the opposite calculus process ofdifferentiation must be applied if the true freeness factor of the pulpis to be obtained. The velocity of drainage cannot, in itself, definepulp freeness since it varies throughout the drainage operation and isdirectly affected by factors other than the freeness of the pulpsuspension.

As a sheet is formed on a screen the liquid initially flows through veryrapidly as only the screen resists its passage. For each unit ofdrainage volume passing through the screen a unit weight of pulpproportional to the consistency of the pulp suspension will be depositedon the screen and will retard further drainage. The degree of suchretardation is uniquely dependent on the character of the pulp. Eachunit of drainage volume passing through the screen also represents acorresponding decrease in the hydrostatic head of the pulp suspensionabove the screen, this hydrostatic head constituting the primary drivingforce which causes the drainage operation to occur. Also, since the pulpparticles in any pulp suspension are of random sizes it also occurs thatthe smaller particles which can pass through the screen or a very thinmat of pulp existing at the beginning of the drainage operation cannotpass through the thicker pulp mat existing later in the drainageoperation. Such smaller particles when caught on the pulp mat will tendto plug up the pulp mat more completely and to retard drainage moresubstantially, so that the retarding effect of the deposition of a unitweight of pulp in the latter partof the sheet-making process will begreater than the corresponding retarding efiect during the. earlier partof the sheet making process. It follows that the degree of difference insuch retarding effects will serve as a definitive indication of therelative proportion of smaller pulp particles, or fines, present in thepulp suspension. This indication is of great importance to thepapermaker as it tells him the extent to which he is cutting pulp fibersinstead of hydrating them. Conventional testers cannot discriminatebetween a freeness value obtained by destructive cutting of fibers andthe same value obtained by proper hydration of uncut fibers.

From the foregoing it can be seen that the drainage operation isaffected by many substantial factors other than the freeness of thepulp. I have discovered that the basic factor which determines thefreeness value of any pulp is the rate of change of free drainagevelocity caused by the deposition of an extremely thin layer of thepulp, and I have devised a method and apparatus which permits: (1) theisolation of this basic factor from myriad other Fourdrinier papermachine operating variables; (2) continuous indication of the factor;(3) continuous indication of any change in the factor caused byvariations in quality of hydration; and (4) control of the refiningmachines to cause them to deliver a pulp of uniform freeness.

To avoid confusion it should be recognized that pulp freenessconventionally has been defined to be the result obtained by testingpulp in some particular device of arbitrary design. In such a case it isobvious that the result obtained will depend upon the particular designof device used as much as it will depend upon the character of the pulptested. This fact accounts for the serious discrepancies in freenessvalues obtained when the same pulp is tested on different conventionaldevices. I have defined true pulp freeness as the reciprocal of the rateof change of free drainage velccity caused by the deposition of anextremely thin layer of the pulp, and this value will be consistent fora particular pulp regardless of the design of any test device so long asit measures the variable soughtl In calculus terms this definition maybe expressed practically as freeness AV and theoretically as freeness05- wnere V represents free drainage velocity, and P represents pulp matthickness.

To avoid confusion it should also be noted that in my use of the termquality of hydration, I am considering good quality of hydration of pulpfibers as that treatment which exposes the fibers to intense gross andmolecular stresses Without causing the mechanical dilapidation of asubstantial proportion of the fibers; and poor quality of hydration asthe similar treatment of the fibers which does cause the mechanicaldelapidation of a substantial proportion of the fibers. I havediscovered that pulp freeness as herein defined, is substantiallyuniform throughout the drainage operation when pulp has been subjectedto good quality hydration, and that the freeness is not uniformthroughout the drainage operation when pulp has been subjected to poorquality hydration. Speaking again in calculus terms the quality ofhydration can be expressed as the reciprocal of the second derivative ofthe free drainage velocity; or, practically 1 quality of hydration oc Fand, theoretically,

- 1 quality of hydration ocfl dP where V represents free drainagevelocity, and P represents pulp mat thickness.

In accordance with my invention the freeness and quality of hydration ofpulp suspensions may be determined independently of the consistency ofthe suspension, by determining the effect on drainage caused by thesettling of fibers on a moving screen or Wire of a Fourdrinier machine.In carrying out my invention, I install a plurality of troughs under theFourdrinier wire at difierent distances from the head box of a papermaking machine which empty into containers of equal dimensions havingdrainage orifices therein of 0 equal size. The first trough is locatednear the head box of the paper machine, at a suflicient distance toallow the preliminary formation of a thin fiber mat on the Fourdrinierwire. A second trough is located closely adjacent to the first troughand the other trough or troughs are lo cated further away from the headbox. Since the drainage velocity decreases throughout the sheet makingoperation there will always be a greater volume of water in the firstcontainer than in the second container. It will be understood that thedrainage orifices in the containers are of such sizes to accommodate thedrainage through the wire and from the troughs after suficient head hasbeen built up. By this means I am enabled to determine simultaneouslythe drainage rate at a plurality of hydrostatic heads and a plurality ofthicknesses Of fiber mat on the wire. At any given condition ofFourdrinier operation the ratio of the volume of liquid collected in thefirst container to the volume of liquid collected in the secondcontainer is proportional to the freeness of the pulp suspension. Thereason for this is that the effects of consistency variation, decreasein drainage velocity caused by decrease of hydrostatic head, variationof water viscosity caused by temperature variation, and similar factorsapply to each trough, whereas the efiect of the pulp mat addedproportional to the drainage into the first trough applies only to thesecond trough. Thus this measurement isolates the variable sought fromthe other variables and determines the deceleration in drainage due topulp freeness during the sheet forming process.

In the accompanying drawings forming a part of this application,

Fig. 1 is a diagrammatic view showing apparatus for determining therates of deceleration in drainage through the Fourdrinier wire atdifferent distances away from the headbox; and

Fig, 2 is a diagrammatic view showing apparatus for indicating the ratiobetween the difference in volume in adjacent containers and thegreaterlvolume.

Referring now to the drawing for a better understanding of my inventionI provide a trough l0 beneath the moving Fourdrinier wire H of apapermaking machine a sufficient distance from the head box 12 to allowthe preliminary formation of a thin fiber mat l3 on the Fourdrinierwire. A second trough M of the same width as trough I0 is providedrelatively close, but further away from the head box I2, than troughII]. The troughs In and I4 discharge the drained liquid through conduitsIll and I4 into containers l6 and I1, respectively, having the samedimensions. The ratio of the volume of liquid collected in container I6to the volume of liquid collected in container I! is proportional to thedeceleration of drainage between the troughs ID and I4 respectively.

Volume 16 Volume l7 deceleration of drainage for the time intervalbetween trough I0 and trough I4.

A second set of similar troughs I3 and I9 may be located similarly totroughs II] and I l but further along the Fourdrinier wire. The troughsl8 and I9 discharge the drained liquid into containers 2I and 22respectively through conduits I8 and I9 respectively. The ratio of thevolume of liquid thus drained into the container 2| to the volumedrained into container 22 is an indication of the rate of change indrainage for the time interval between troughs I8 and I9. A comparisonof the ratio of volumes drained in troughs I0 and I 4 with the ratio ofvolumes drained in troughs l8 and I9 is proportional to the change indeceleration of drainage velocity between said pairs of troughs. Thiscomparison of ratios gives the change of freeness during the sheetforming process and indicates to the paper maker the quality ofhydration of the pulp on the paper machine. The reason for this is thatgood quality hydration leaves the greater proportion of fibers intact sothat the mechanics of sheet formation are substantially uniformthroughout the sheet forming process; whereas, poor quality hydrationcauses a greater proportion of fibers to become dilapidated or cut intotiny pieces fines and these fines pl-ug up the true pulp mat to increasedrainage retardation in the later stages of sheetmaking, which in turncauses a false (and lower) freeness value to be obtained in the laterstages of the sheet making process.

When a pulp suspension of high freeness is used on the paper machine arelatively large volume of liquid will be collected in container I6 and,because the drainage retarding effect of such pulp is small, the volumeof liquid collected in container I! will also be relatively large. Theratio Volume 16 Volume 1 7 is in such case low and is inverselyproportional to the freeness of the pulp. When a pulp suspension of lowfreeness is used on the paper machine the volume of liquid collected incontainer I6 is less than in the first case, and the volume of liquidcollected in container I1 is proportionately much less than in the firstcase because of the substantially greater drainage retarding effect ofthe slow pulp. The ratio Volume 16 Volume 17 with slow pulp, therefore,is high and thus indicates lower freeness of the pulp suspension.

This method of determining the freeness of pulp suspensions is affectedvery little by variations in consistency since the volume dischargedfrom each trough into its associated container 6 will vary inversely asthe consistency varies without affecting the ratio of Volume 16 Volume17 which is the primary variable desired.

To obtain the rate of deceleration of drainage velocity from the volumeof liquid collected the following apparatus may be employed. Referringto Fig. 1, the containers I6 and I! are substantially of the samedimensions and are separated by a common wall in the form of a plate 23having a hinge 24 at the bottom thereof. The compartments thus formedare sealed apart by a flexible diaphragm 26. Both compartments areprovided with drainage orifices 21 and 21' of the same size and of suchsize that the drainage from the compartments is restricted permitting.the building up of a hydrostatic head therein. When the volume incontainer I6 is greater than the volume in the container I1 a higherhydrostatic head will exist in container IS. The volume in container I6is always greater because the liquid drains faster when the sheet isfirst formed. At 28 I show an air jet which is located closely adjacentand is directed toward the movable wall .or plate 23. The air jet 28 isattached to an air line 29 which communicates with an air pump 3 I, apressure indicator 32, and a bellows 33, The bellows 33 bears againstthe plate 23 so that when pressure builds up in the bellows the plate ispushed away from the jet. If the pressure in the bellows 33 builds upsufiiciently so that, aided by the volume in container I! it overcomesthe pressure of the volume of liquid in compartment I6, the plate orwall 23 moves away from the jet 28 and'the pressure in the airlinedrops, until an equilibrium is established between the force exerted bythe liquid in container I1 and the bellows 33 and the higher hydrostatichead in container I6. The pressure indicated on the pressure indicatoris a function of Volume 17 or rate of deceleration. This device may alsobe used to obtain the rate of deceleration between troughs I8 and I9.

The change in rate of deceleration for the time interval between troughsI0 and I4 and the troughs I8 and I9 may easily be determined byconnecting the pressure line 29 and the pressure line 29 associated withthe troughs l8 and [9 to a differential pressure gauge 34.

It will be seen that with the apparatus so far described, the volumes ofwater draining into the troughs and their associated containers willdepend upon the speed of the Fourdrinier wire, so that, to evaluate thedata obtained, separate ratios would have to be calculated for eachspeed at which the machine is operated.

constant the value of which is determined by the freeness and quality ofhydration of the pulp suspension, where It represents the indicated rateof drain-age or hydrostatic head in the first container away from thehead box and hi the indicated-rate of drainage or hydrostatic head inthe second container. In accordance with my invention, I have providedmeans whereby this ratio is indicated constantly during the operation ofthe paper machine by means of a Wheatstone bridge.

Referring now to Fig. 2 of the drawing I show apparatus adapted forindicating the free ness factor, continually, as above set forth. At 40I show a source of direct current, such as a battery, one terminal ofwhich is connected by means of a flexible connection 4| to the slidingcontact 42 of a slide'wire bridge divided into resistor portions 43a and43b by the contact 42. The contact 42 is moved back and forth along theresistor portions, as hereinafter described, by means of a reversiblemotor 44 adapted to be energized from a circuit 46. Connected toresistor portion 43b is a wire 4'! which leads toa resistor 48 andthence through a wire 49 to the other terminal of the battery 46. Thewire 41 is also connected by a wire to one connection of the coil of apolarized relay 6|. Mounted in the container I6 is a float 5| which isconnected to and insulated from a sliding contact 52 for the resistor48. The contact 52 is mounted on a conducting bar 53 which is connectedat its upper end to the upper end of the resistance coil of the resistor48 and to the wire 49. Accordingly, the resistance circuits 41, 48 and49 varies directly in response to the hydrostatic head in the containerl6.

Connected to the upper end of portion 43a of the resistance element is awire 54 which is connected to one end of the resistance element of aresistor 56, the other end being connected to the wire 49 leading backto the battery 46. The resistance in the resistor 56 is varied by meansof a sliding contact 51 mounted on a conducting bar 53, which isconnected at its opposite end to the wire 54 and to the end of theresistance element of resistor 56. It is also connected to a wire 59leading to the other connection of the coil of the polarized relay 6|.

The sliding contact 51 is-operated by means of an air cylinder 52 havinga piston 63 therein which is connected to the sliding contact 51 bymeans of a rod 64 and adjusting nuts 66. The contact 57 is separated andinsulated from the rod 64 as by means of insulating material 61. Aspring 63 is mounted on the rod 64 and bears against a fixed abutment 69at its outer end and against a collar I! mounted on the rod 64 at itsopposite end. The cylinder 62 is connected to the conduit 29, alreadydescribed, in which the pressure varies directly responsive to thedifference in hydrostatic head of the water in container Hi and that incontainer Thus, the resistance in resistor 56 varies directly responsiveto the difference in hydrostatic heads in the two con tainers.

It will be seen that the circuits described comprise a Wheatstone bridgewhich includes as one side resistance portion 43b of the potentiometer45 and as a second side the resistor 48; as the third side the resistor'56, and as the fourth side the upper resistance portion 43a of theslide bridge 45. The cross circuit includes the wires 59 and 55 and thecoil of the polarized relay 6|. Whenever the resistance in the resistor48 is in the 8 greater than that in resistor 56, current will flow fromthe battery through 4|, 43a, 54, and 59, and through the polarized relay6|. When the resistance is greater in the resistor 56 than in 48, thecurrent will flow from the battery hrough 4|, 43b, 41 and 55 through therelay 6|.

The relay 6| controls the circuit to the motor 44 asfollows. Associatedwith the relay 6| is a switch having contacts 16 and 11 controlled bythe armature of the relay 6| constituting a switch arm 15 which isconnected at 18 to a common wire 19 leading to the motor. The contact I6is connected to a wire 8| leading to the motor 44 and the contact 11 isconnected to a wire 82 leading to the motor 44.

It will be seen that when the relay 6| is energized to actuate itsarmature, which is the switch arm 15, upwardly, as viewed in thedrawing, the motor 44 will be energized through the wires 8| and 19 torun in one direction and when the relay BI is energized to move thearmature l5 downwardly to engage the contact 11, the motor 44 will beenergized to run in the opposite direction. Connected to the motor 44 isa threaded shaft 83 upon which is mounted a nut 86 connected to apointer 31 which is connected to and insulated from the sliding contact42 of the slide bridge 45. At 85 is shown a graduated scale whichindicates the relative resistances in the circuits hereinbeforedescribed, and accordingly the freeness of the pulp. Inasmuch as theratio between the difference in heads in containers I6 and I! and thehead in container I6 is a constant, independently of the velocity ofmovement of the wire II, the indication of the pointer 8! will be aconstant the value of which stands in the relation of From the foregoingit will be apparent that I have devised an improved method and apparatusfor determining the freeness of pulp suspensions during the manufactureof paper which indicates the freeness and quality of hydration of thepulp, and which is substantially unaffected by the consistency of thepulp suspension.

While I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications, without departing from the spiritthereof, and I desire, therefore, that only such limitations shall beplaced thereupon as are specifically set forth in the appended claims.

What I claim is:

1. The method of determining the freeness of paper pulp suspensionswhile a sheet is being formed on a Fourdrinier wire comprising,collecting the drained liquid at at least two different positionsbeneath the sheet, and measuring the ratio of drainage between saidpositions.

2. The method of determining the freeness of paper pulp suspensionswhile on the wire of a Fourdrinier paper machine having a head boxcomprising collecting the drained liquid at a pair of adjacent positionsalong the moving Fourdrinier wire a sufficient distance from the headbox to allow a preliminary mat of fiber to form thereon, collecting thedrained liquid at a second pair of adjacent positions further along saidwire, and measuring the ratio of deceleration of drainage at said pairsof points.

3. Apparatus for determining the freeness of paper pulp suspensionswhile on the wire of a Fourdrinier paper machine having a head box,comprising a trough positioned beneath the wire a short distance fromthe head box to allow the preliminary formation of a thin fiber mat onsaid wire and disposed to receive liquid draining through the wire intosaid trough, a second trough positioned under said Fourdrinier wirefurther away from the head box than the first trough and also disposedto receive liquid draining through the wire, a pair of equal dimensionalreceptacles communicating with said troughs, and having restricteddrainage orifices of equal size in the lower portions thereof, and meansindicating the ratio between volumes of liquid collected in the tworeceptacles.

4. Apparatus for determining the freeness of paper pulp suspensionswhile on the wire of a Fourdrinier paper machine having a head box,comprising a trough positioned beneath the wire a short distance fromthe head box to allow the preliminary formation of a thin fiber mat onsaid wire and disposed to receive liquid draining through the Wire intosaid trough, a second trough positioned under said Fourdrinier wirefurther away from the head box than the first trough and also disposedto receive liquid draining through the Wire, a receptacle communicatingwith each trough, said receptacles each having a restricted orifice inthe lower portion thereof, the orifices being of equal size and sorestricted to permit the building up of a hydrostatic head in thereceptacles, and means to indicate the difierence in hydrostatic head inthe two receptacles.

5. Apparatus for determining the freeness of paper pulp suspensionsWhile on the wire of a Fourdrinier paper machine having a head box,comprising a trough positioned beneath the wire a short distance fromthe head box to allow the preliminary'formation of a thin fiber mat onsaid wire and disposed to receive liquid draining through the Wire intosaid trough, a second trough positioned under said Fourdrinier wirefurther away from the head box than the first trough and also disposedto receive liquid draining through the wire, a pair of equal dimensionalreceptacles communicating with said troughs and having restricteddrainage orifices of equal size in the lower portions thereof, a movablewall disposed to seal the containers apart, an air pump, an air jetcommunicating with said pump and sealed against said movable wall whenthe hydrostatic head in the container opposite the jet is greater thanthe hydrostatic head on the side adjacent the jet, a bellowscommunicating with said pump and disposed to push the wall away from thejet thereby causing the pressure to vary in said air line, and apressure gauge communicating with said air lines.

6. Apparatus for determining the freeness of paper pulp suspensionswhile on the moving wire I of a Fourdrinier paper machine having aheadbox, comprising a pair of troughs positioned beneath the wire asuficient distance from the head box to allow a preliminary formation ofa thin fiber mat on said wire and disposed to receive liquid drainingthrough the wire above said troughs, a second pair of troughs furtheraway from the head box than the first two troughs and also disposed toreceive the liquid draining through the wire above said second pair oftroughs, a pair of equal dimension receptacles communicating with eachpair of troughs and having restricted drainage orifices of equal size inthe lower portions thereof, means indicating the rates of decelerationof drainage in the respective pairs of receptacles, and other meansindicating the change in rates of deceleration occurring between saidpairs of receptacles.

'7. Apparatus for determining the freeness of paper pulp suspensionswhile on the moving wire of a Fourdrinier paper machine havin a headbox,comprising a pair of troughs positioned beneath the wire a sufiicientdistance from the head box to allow a preliminary formation of a thinfiber mat on said wire and disposed to receive the liquid drainingthrough the wire above said troughs, a second pair of troughs furtheraway from the head box than the first two troughs and also disposed toreceive liquid draining through the wire thereabove, a pair of equaldimensional receptacles communicating with each pair of troughs andhaving restricted drainage orifices of equal size in the lower portionsthereof, a movable wall separating each pair of receptacles, an air pumpfor each pair of troughs, an air jet communicating with each pump andsealed against said movable wall when the hydrostatic head in thecontainer opposite the jet is greater than the hydrostatic head on theside adjacent the jet, a bellows communicating with each pump anddisposed to push the wall away from the jet thereby causing the pressureto vary in said air lines, and a difierential pressure gaugecommunicating with both of said air lines.

WILLIAM G. REYNOLDS.

REFERENCES (JIEED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,573,850 Naiman Feb. 23, 19261,701,331 Merrill Feb. 5, 1929 2,379,835 Sisler July 3, 1945 2,442,888Cram June 8, 1948

